The present invention relates to sharing of home base stations in wireless networks. More particularly, and not by way of limitation, the present invention is directed to a system and method to support sharing of home base stations among multiple cellular networks via enhanced handling of Closed Subscriber Group (CSG) related information in System Information (SI).
The usage of mobile broadband services using cellular networks has shown a significant increase during recent years. In parallel to this, there is an ongoing evolution of Third Generation (3G) and Fourth Generation (4G) cellular networks like High Speed Packet Access (HSPA), Long Term Evolution (LTE), Worldwide Interoperability for Microwave Access (WiMAX), etc., to support ever-increasing performance with regards to capacity, peak bit rates and coverage. Operators deploying these networks are faced with a number of challenges, e.g., related to site costs and availability, transport costs and availability, lack of wireless spectrum, etc. Many different techniques are considered for meeting these challenges and providing cost-efficient mobile broadband.
One option available to the operators is to use shared network infrastructure and sites, especially when multiple cellular operators agree to deploy their network together. This is beneficial since it reduces the total deployment costs, and can provide benefits due to pooling of the available spectrum. One drawback with network sharing in its current form is that it requires quite a lot of cooperation between the operators sharing the network. Because the network configuration is common for a part of the network that is shared, it may make it difficult to differentiate the treatment of users from each operator. The sharing of a part of the network may also make interaction (e.g., handover) with non-shared part more complex, since the shared part needs to interact with multiple non-shared networks (managed by multiple operators).
The support for network sharing has been enhanced in the Third Generation Partnership Project's (3GPP) Universal Terrestrial Radio Access Network (UTRAN) and Evolved UTRAN (E-UTRAN) standards and is defined in, for instance, 3GPP's Technical Specifications (TS) 23.251, 23.401 and 36.300 (these and other specifications may be obtained at ftp://ftp.3gpp.org/Specs/latest). The UTRAN and E-UTRAN standards allow different scenarios for network sharing, but it is expected that a common scenario will be when the Radio Access Network (RAN) is shared and each operator has its own Core Network (CN). This scenario, which is called Multi-Operator Core Network (MOCN) in 3GPP, is illustrated in FIG. 1. In the MOCN configuration of FIG. 1, an operator X's RAN 10 is shared by operator-specific Core Networks 12-14 from three different operators—operator A, operator B, and operator C. In an MOCN configuration, multiple CN nodes (e.g., nodes 12-14) may be connected to the same Radio Network Controller (RNC) (not shown) in the shared RAN (e.g., RAN 10 in FIG. 1), even when these CN nodes are operated by different network operators. It is observed here that MOCN is a network-sharing configuration in which only the RAN is shared, as opposed to Gateway Core Network (GWCN)—a network-sharing configuration in which parts of the operator core networks are also shared.
From a technical point of view, the MOCN configuration uses the multi-to-multi connectivity of the UTRAN's Iu (as described, for example, in 3GPP TS 25.413) and E-UTRAN's S1 (as described, for example, in 3GPP TS 36.413) interfaces between the RAN and CN as exemplarily illustrated by the dotted line 16 in FIG. 1. The MOCN configuration thus makes it possible to connect a RAN node (e.g., an RNC or an Evolved Node-B (eNB or eNodeB) (not shown in FIG. 1)) to multiple CN nodes (e.g., Serving GPRS Support Node (SGSN) wherein “GPRS” refers to General Packet Radio Service, Mobility Management Entity (MME), etc.) belonging to different operators. The RAN will, in this configuration, broadcast one Public Land Mobile Network (PLMN) identity (ID) for each operator sharing the RAN (as described, for example, in TS 25.331 and TS 36.331). As is known, a PLMN is a wireless communication system (e.g., a cellular telephone network) operated by a network operator and intended for use by terrestrial subscribers in vehicles or on foot. In response to RAN's broadcast of PLMN IDs, the User Equipment (UE) or mobile handset will, at initial attach, select which PLMN it wants to connect to, and the RAN will make sure that the initial attach signaling is routed to the correct operator's CN (as described, for example, in TS 23.401 and 23.060). Once the UE has been assigned a CN node, there are also mechanisms making it possible for the RAN and CN to route subsequent signaling related to this UE to the same CN node. Besides the list of PLMN IDs, almost all of the rest of the system information (as described, for example, in TS 25.331 and 36.331) broadcasted on the cell broadcast channel (e.g., the Physical Broadcast Channel (PBCH)) in the shared RAN is common for all operators sharing the RAN. However, currently there are a few exceptions to this common treatment for all operators. For example, in E-UTRAN, the parameter “cellReservedForOperatorUse” is per PLMN (i.e., it is an operator's PLMN-specific). Similarly, in UTRAN, the parameters “Domain Specific Access Restriction Parameters For Operator N” and “Paging Permission with Access Control Parameters For Operator N” are also per PLMN.
Another option available to an operator for network-sharing is the deployment of home base stations (e.g., Home eNB or HeNB (in LTE), Home Node-B or HNB (in HSPA), or a femtocell (as this names is used by www.femtoforum.org)) or other small base stations complementing the traditional macro cellular network. Possible benefits of these small base stations or home base stations are lower site costs due to smaller physical size and lower output power, as well as increased capacity and coverage due to the closer deployment to the end user. The operator can configure the cells with these smaller base stations as Open, Hybrid or Closed. Open cells are possible to use for all subscribers, with no preference to perform cell reselection of individual cells. Closed cells broadcast a Closed Subscriber Group (CSG) cell type (called “CSG Indication” that can either indicate values “true” or “false”) and CSG identity (called “CSG ID” that may be a 27-bit identifier). Closed cells are only available for mobile handsets or UEs belonging to the specific CSG. When the cell is closed, the CSG Indication broadcasted has the value “true”. In addition, users belonging to a CSG have a preference for selecting CSG cells with the same CSG ID. Hybrid cells, on the other hand, may broadcast a CSG ID value, but the CSG Indication broadcasted has the value “false”. Thus, hybrid cells may be available for all users.
Since it is expected that the number of home base stations could be very large and that they are considered less reliable nodes, solutions have been introduced in 3GPP's E-UTRAN and UTRAN standards for home base stations to connect to the CN via a home base station gateway (GW) (e.g., the H(e)NB GW in E-UTRAN or HNB GW in UTRAN). The H(e)NB GW or HNB GW has the functionality to hide the home base station from the rest of the network.
In the LTE/System Architecture Evolution (SAE) case, the HeNB GW is optional and therefore has S1-interfaces on both sides of it. FIG. 2 shows an HeNB logical architecture in which an HeNB GW 18 is shown connected to an HeNB 20 and a Core Network 22 via S1 interfaces 23 and 24, respectively. When HeNB GW is implemented, for the rest of the network, the HeNB GW just looks like a large eNB with many cells. From the HeNB point of view, the HeNB GW looks like a CN node (MME). The HeNB may only connect to one HeNB GW and, in this case, the HeNB may not have the network node selection functionality that can allow the HeNB to connect to multiple HeNB GW nodes. Instead, the HeNB GW supports the network node selection functionality enabling support for MME-pools (e.g., from multiple Core Networks). On the other hand, when the HeNB connects directly to the CN (i.e., when HeNB GW is omitted), the HeNB may itself support the network node selection functionality.
In the HSPA/Wideband Code Division Multiple Access (WCDMA) case, the HNB GW is mandatory. A new Iuh-interface is defined between the HNBs and the HNB GW, and the normal Iuh-interface is used between the HNB GW and the CN. FIG. 3 depicts an HNB logical diagram in which an HNB GW 26 is shown connected to an HNB 28 via an Iuh interface 29 and to a Core Network 30 via an Iu interface 32. When HNB GW is present, for the rest of the network, the HNB GW just looks like a large RNC with, potentially, many service areas (that is the UTRAN concept for one or multiple cells). The HNB only connects to one HNB GW, and the HNB does not have the network node selection functionality that can allow the HNB to connect to multiple HNB GW nodes. Instead, the HNB GW supports the network node selection functionality enabling support for Mobile Switching Center (MSC)- and SGSN-pools (e.g., from multiple Core Networks).